1. Field of the Invention
The present invention relates to a suck back valve capable of preventing liquid drip of a fluid from occurring at a supply port, by sucking a prescribed amount of fluid flowing through a fluid passage based on a displacement operation of a diaphragm.
2. Description of the Related Art
There has hitherto been known, for example, a semiconductor wafer manufacturing process in which a suck back valve is employed. In the suck back valve, when supply of a coating liquid to the semiconductor wafer is halted, there is a function for preventing so called liquid drip, wherein minute amounts of coating liquid drip from a supply port onto the semiconductor wafer.
The suck back valve according to such a conventional technique is shown in FIG. 5 and is disclosed, for example, by Japanese Utility Model Publication No. 8-10399.
Such a suck back valve 1 comprises a main valve body 5 formed with a fluid passage 4 interconnecting a fluid inlet port 2 and a fluid outlet port 3, and includes a bonnet 6 connected to an upper portion of the main valve body 5. A diaphragm 7 made up of a thick-walled portion and a thinwalled portion is disposed in the center of the fluid passage 4. An unillustrated pressurized fluid supply source is connected to the bonnet 6, the bonnet further being formed with a pressurized fluid supply port 8 for supplying pressurized air for operating a diaphragm under a switchover action of a directional control valve (not shown).
A piston 9 is fitted to the diaphragm 7, with a v-packing 10 installed in the piston 9 and slidable along an inner wall surface of the main valve body 5 and serving a sealing function. Further, a spring 11 which normally presses the piston in a upward direction, is disposed in the main valve body 5.
An adjusting screw 12 is disposed on the top of the bonnet 6, which, by increasing or decreasing a screw-in amount thereof, abuts against the piston 9 and adjusts a displacement amount of the piston 9, whereby the amount of coating liquid sucked by the diaphragm 7 is adjusted.
A coating liquid supply source 13 storing therein a coating liquid is connected to the fluid inlet port 2 through a pipe 14. Further, between the coating liquid supply source 13 and the fluid inlet port 2, and ON/OFF valve 15, which is constructed as a separate body apart from suck back valve 1, is connected. The ON/OFF valve undertakes a function for switching between a supply condition and a supply-halted condition of the coating liquid to the suck back valve 1, based on energizing and deenergizing actions of the ON/OFF valve 15.
Operation of the suck back valve 1 shall now be explained in outline. In an ordinary state in which the fluid is supplied from the fluid-inlet port 2 to the fluid-outlet port 3, the piston 9 and diaphragm 7 are displaced downwardly in an integrated manner in accordance with action of the pressurized fluid supplied from the pressurized fluid supply port 8. The diaphragm 7, which is coupled to the piston 9, protrudes into the fluid passage 4 as shown in FIG. 5 by the two-dot-chain line.
When flow of fluid through the fluid passage 4 is halted, the piston 9 and diaphragm 7 are raised in unison under the action of an elastic force exerted by the spring 11, by stopping the supply of pressurized fluid from the pressurized fluid supply port 8. A predetermined amount of fluid remaining in the fluid passage 4 is sucked under action of a negative pressure produced by the diaphragm 7. Thus, dripping of liquid, which would otherwise be caused at an unillustrated fluid supply port, is prevented.
In this instance, the suck back amount of the coating liquid corresponds with displacement of the piston 9, wherein a displacement amount of the piston 9 is adjusted by the screw element 12.
Incidentally, with the suck back valve 1 in accordance with the conventional technique, for adjusting the flow amount of pressurized air supplied by the pressurized fluid supply port 8, a speed controller or similar flow control valve 17 is connected thereto through a conduit 16 such as a tube. The flow amount control valve 17 adjusts the flow of pressurized fluid flowing therein by changing the flow passage area inside of the valve.
However, in the suck back valve 1 according to the conventional technique, the flow amount of pressurized air supplied by the pressurized fluid supply port 8 is controlled via a mechanical means, such as the above-described flow amount control valve 17, and therefore, there is a disadvantage that fine control of the flow amount of pressurized air supplied by the pressurized fluid supply port cannot be achieved.
Further, in the suck back valve according to the conventional technique, since adjustment of a suck back amount of the coating liquid is performed manually by increasing/decreasing a screw-in amount of a screw member 12, there results the disadvantage that the coating liquid suck back amount cannot be precisely controlled. In this case, a screw-in amount of the screw element which has been formerly set has to be reset each time corresponding to a desired coating liquid suck back amount, adding further complexity to the system.
Furthermore, when using the conventional suck back valve 1, piping connection operations become necessary between the suck back valve 1 and the flow amount control valve 17, as well as between the suck back valve 1 and the ON/OFF valve 15, resulting in further inconvenience. In addition, dedicated space becomes necessary for attachment of the flow amount control valve 17 and the ON/OFF valve 15, respectively, externally apart from the suck back valve 1, with the disadvantage that the installation space has to be increased overall.
Still further, flow passage resistance is increased as a result of additional piping connected between the suck back valve 1 and the flow amount control valve 17, with the disadvantage that response accuracy (responsiveness) of the diaphragm 7 is deteriorated.
Still further, a driving apparatus for switching the ON/OFF valve 15 between ON and OFF states must be separately provided, so that along with further piping connection operations for interconnecting the ON/OFF valve 15 and the driving apparatus, there is the disadvantage of soaring costs for the apparatus overall.
Further, in the case that the diaphragm is displaced using an unillustrated electrical means, there is the fear of changes occurring in the characteristics of the fluid flowing inside the fluid passage under action of a heat amount generated by the electrical means.